Identification of an additional member of the protein-tyrosine-phosphatase family: evidence for alternative splicing in the tyrosine phosphatase domain.

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Abstract
Protein-tyrosine-phosphates (protein-tyrosine-phosphate phosphohydrolase, EC 3.13.48) have been implicated in the regulation of cell growth; however, to date few tyrosine phosphates have been characterized. To identify additional family members, the cDNA for the human tyrosine phosphate leukocyte common antigen (LCA; CD45) was used to screen, under low stringency, a mouse pre-B-cell cDNA library. Two cDNA clones were isolated and sequence analysis predicts a protein sequence of 793 amino acids. We have named the molecule LRP (LCA-related phosphates). RNA transfer analysis indicates that the cDNAs were derived from a 3.2-kilobase mRNA. The LRP mRNA is transcribed in a wide variety of tissues. The predicted protein structure can be divided into the following structural features: a short 19-amino acid leader sequence, an exterior domain of 123 amino acids that is predicted to be highly glycosylated, a 24-amino acid membrane-spanning region, and a 627-amino acid cytoplasmic region. The cytoplasmic region contains two .apprxeq.260-amino acid domains, each with homology to the tyrosine phosphatase family. One of the cDNA clones differed in that it had a 108-base-pair insertion that, while preserving the reading frame, would disrupt the first protein-tyrosine-phosphatase domain. Analysis of genomic DNA indicates that the insertion is due to an alternatively spliced exon. LRP appears to be evolutionarily conserved as a putative homologue has been identified in the invertebrae Styela plicata.